This invention relates to batteries, and more particularly to batteries having an electrode comprised of a particulate active electrode material and a binder.
Non-aqueous batteries, i.e. batteries having a non-aqueous electrolyte, including both non-aqueous primary batteries and non-aqueous secondary batteries, are well known and commonly used, especially in advanced electronic appliances, such as portable personal computers, compact video cameras, and pocket or cellular telephones. Certain non-aqueous primary batteries, such as those having lithium as an active anode material, have various advantages over other primary batteries, such as high voltage, high energy density with low self-discharge, and extremely long storage life. Certain non-aqueous secondary batteries have improved charge and discharge characteristics such as improved charge and discharge capacity, as well as excellent cycle life and stability.
Commercially available non-aqueous batteries typically include at least one electrode that is made of a particulate active material that is held together by a binder comprising one or more polymers. The polymers commonly used in binders for making electrodes for non-aqueous batteries are generally insoluble in water and are not dispersible, or at least not easily dispersible, in water. Examples of polymers that are used as binders for an electrode in a non-aqueous battery include ethylene-propylene copolymer; a terpolymer of ethylene, propylene and a diene (EPDM); polytetrafluoroethylene (PTFE); and polyvinylidene fluoride (PVDF). A disadvantage with binders comprised of polymers that are not water soluble or water dispersible is that organic solvents must be used during preparation of the electrode. The use of organic solvents is undesirable on account of the relatively high costs associated with environmentally compliant handling and disposal of the organic solvents.
Accordingly, the use of water-soluble and/or water-dispersible polymers as binders for preparing electrolytes from particulate active materials is highly desirable. Known water-soluble polymers suitable as binders for electrodes include carboxymethyl cellulose and poly(acrylic acid). However, the known binders comprising one or more water-soluble or water-dispersible polymers have not exhibited satisfactory adhesive properties for use in batteries.
Good adhesion is necessary to prevent disintegration of the electrode or separation of the electrode material from a metallic carrier.
In addition to good adhesion, the binder must also be resistant to the organic solvent of the electrolyte. For example, the binder must not soften, dissolve or decompose when contacted by the non-aqueous electrolyte. Further, the binder must not react with the anode or cathode active materials, which may include highly oxidizing materials such as MnO2 or LiMn2O4, and highly reducing materials such as lithiated carbonaceous materials. Another requirement is that the binder must exhibit sufficient flexibility to withstand expansion and/contraction of the electrode during discharge. In the case of secondary batteries, the binder must exhibit resilient flexibility to withstand many cycles of alternating expansion and contraction associated with charging and discharging the battery.
The known binders comprised of one or more water-soluble and/or water-dispersible polymers have not exhibited an excellent combination of chemical resistance, adhesiveness, flexibility, and resilience.
This invention pertains to a water-soluble binder for an electrode in a battery; an aqueous binder solution useful for preparing an electrode for a battery; an electrode mixture useful for preparing an electrode for a battery; a process for making an electrode for a battery; an electrode for a battery; and a battery. The binder of this invention exhibits excellent chemical resistance to electrolytes, including non-aqueous electrolytes, and excellent chemical resistance to active electrode materials, including active electrode materials commonly employed in primary and secondary non-aqueous batteries. The binder in the invention also exhibits excellent adhesive properties, flexibility and resilience. As a result of these properties, the binders of this invention are well suited for use in preparing electrodes for a wide variety of batteries, including both primary and secondary batteries, batteries having aqueous or non-aqueous electrolytes, and batteries having sheet-like electrodes arranged in complicated geometries, such as spirally wound batteries.
The water-dispersible binders of this invention comprise polyacrylamide, and at least one copolymer selected from the group consisting of carboxylated styrene-butadiene copolymer and styrene-acrylate copolymer.
The aqueous binder solution of this invention is comprised of water, polyacrylamide, and at least one copolymer selected from the group consisting of carboxylated styrene-butadiene copolymer and styrene-acrylate copolymer.
The electrode mixture of this invention comprises an aqueous binder solution containing water, polyacrylamide, and a copolymer selected from the group consisting of carboxylated styrene-butadiene copolymer and styrene-acrylate copolymer; and an active electrode material.
The invention also encompasses a process for making an electrode for a battery. The process comprises the steps of providing an aqueous binder solution, combining and mixing the aqueous binder solution with an active electrode material to obtain a formable electrode mixture, shaping the electrode mixture into a desired electrode form, and removing the water from the desired electrode form to make the electrode. The aqueous binder dispersion includes water and a water-dispersible binder. The water-soluble binder includes polyacrylamide and at least one copolymer selected from the group consisting of carboxylated styrene-butadiene copolymer and styrene-acrylate copolymer. The invention also encompasses the resulting electrode.
In accordance with another aspect of the invention a battery is provided with comprises a positive electrode, a negative electrode, and an electrolyte, wherein at least one of the positive electrode and the negative electrode is comprised of an electrode mixture containing an active electrode material and a binder, in which the binder contains polyacrylamide and at least one copolymer selected from the group consisting of carboxylated styrene-butadiene copolymer and styrene-acrylate copolymer.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.